The present invention relates to a charge indicator for an accumulator or battery that includes a liquid electrolyte.
Charge indicators are used for indicating the state of charge of the accumulator, such as, for example, of a lead accumulator (e.g., a lead-acid battery), in a simple manner readable on the observation area of the transparent inspection rod. This makes use of the fact that the specific weight of the electrolyte changes in dependence on the state of charge.
In the ball guidance channel, at least one ball having a specific weight is guided which matches the specific weight of the electrolyte at a predetermined state of charge. With a correct charge of the battery, the ball is lighter than the electrolyte and floats up in the oblique ball guidance channel. When the accumulator is discharged, the specific weight of the electrolyte drops and is lower than the specific weight of the ball so that the ball sinks down in the ball guidance channel.
DE 25 11 426 C2 discloses a charge indicator with oblique ball guidance channel which ends at the tip of the inspection rod. With an adequate charge of the accumulator, the ball floats up and becomes visible at the end of the inspection rod through the observation area at the first end. If the ball is colored, this makes it possible to implement a colored indication for the correct state of charge. Due to the reflection area at the second end of the inspection rod, an adequate filling level of the accumulator with the electrolyte also becomes visible. In the case where the electrolyte level has dropped to such an extent that the tip of the inspection rod is no longer immersed in the electrolyte, the conical areas of the tip of the inspection rod form a boundary face with air. A total reflection then occurs at the conical areas of the tip of the inspection rod so that the tip appears as a reflecting area, that is to say bright. When the filling level of the electrolyte is adequate and the material of the inspection rod is selected in such a manner that the coefficients of refraction of the inspection rod and of the electrolyte are approximately equal, no further total reflection is produced. There is thus an optical connection via the tip of the inspection rod to the dark inner space of the accumulator so that a dark area appears at the observation area.
EP 1 120 641 A2 and DE 102 24 662 C1 disclose a charge indicator of the type initially mentioned, with a ball guidance channel extending beyond the height of the tip of the inspection rod in the direction of the upper boundary wall of the ball cage. The ball guidance channel accommodates two balls with different specific weight which have different colors. In the discharged state of the accumulator, both balls are located at the lower end of the ball guidance channel as a result of which the upper ball comes to lie underneath the tip of the inspection rod. If there is sufficient electrolyte, the color of the upper ball (e.g., red) becomes recognizable at the observation area of the inspection rod. This indicates that the accumulator is discharged. In a medium state of charge, the upper ball floats up with lower specific weight than the lower ball and disappears from the field of view of the tip of the inspection rod to the upper end of the ball guidance channel whereas the lower ball due to its earlier specific weight does not yet float up in the ball guidance channel. Instead, the lower ball remains at the lower end of the ball guidance channel outside the field of view of the inspection rod. With an adequate electrolyte level, the color of the housing now becomes visible at the observation area. With a good state of charge, the lower ball also floats up and butts against the upper ball which has already floated up as a result of which it is positioned underneath the tip of the inspection rod. At the observation area, the color of the lower ball, e.g. green, is visible as a signal of a good state of charge.
One issue associated with certain conventional charge indicators is that gas bubbles are caught in the area of the tip in the inspection rod and cannot be removed. In the case of charge indications with one ball, it may happen that a gas bubble stays caught in front of the tip of the inspection rod and prevents the ball from rising to the tip of the inspection rod. In the case of charge indicators with two balls, the upper ball can get caught at the tip and be prevented from rising further beyond the tip in the direction of the upper boundary wall. This leads to an erroneous indication in the case of accumulators which are actually functional.